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Cosmoline is the genericized trademark for a common class of brown wax-like petroleum-based rust inhibitors, typically conforming to United States Military Standard MIL-C-11796C Class 3. They are viscous when freshly applied, have a slight fluorescence, and solidify over time and exposure to air.
This section needs expansion with: cosmoline's invention and production. You can help by adding to it. (September 2017)
Chemically, cosmoline is a homogeneous mixture of oily and waxy long-chain, non-polar hydrocarbons. It is always brown in color, but can differ in viscosity and shear strength. Cosmoline melts at 113–125 °F (45–52 °C) and has a flash point of 365 °F (185 °C).
This section needs expansion with: cosmoline's application and storage. You can help by adding to it. (September 2017)
Cosmoline is also frequently applied to automotive disc brake rotors at the factory, to prevent corrosion inside the box before the rotor is placed into service on a vehicle. It is easily removed by spraying brake cleaner on the braking surfaces of the rotor.
During World War II cosmoline was used to coat weapons, including entire tanks, for long sea voyages, to prevent corrosion in salty maritime conditions. U.S. Coast Artillerymen serving the huge coastal artillery batteries were known as "Cosmoliners" as they were regularly assigned the task of "greasing down" their big guns.
Cosmoline was also used during the Pacific island campaigns in World War II by the United States Marines, who sang a song about it to the tune of the popular big-band hit Tangerine: "Cosmoline...keeps my rifle clean". Many felt that it had been invented not merely to prevent rust on their weapons but for making soldiers' lives miserable.
Aging and removal
Freshly applied cosmoline, or that which is hermetically sealed in a plastic bag or shrink wrap, retains its grease-like viscosity and wipes near clean with a rag, leaving only a thin film behind. Older cosmoline which has had air exposure usually solidifies after a few years, once its volatile hydrocarbon fraction evaporates and leaves behind only the waxy remainder. This solid wax does not readily wipe off. It can be removed with laborious scraping but leaves crumbs to be swept or vacuumed away. Application of gentle heat sufficient to melt the waxy hydrocarbons allows cosmoline to drip off. Penetrating oil (such as WD-40 or CRC 5-56 CLP) sprayed and allowed to soak in until cosmoline is restored to a viscous-fluid state allows it to be wiped off. A closed-cabinet parts washer may be used to power wash smaller items. An aqueous rather than petrochemical based wash requires high heat, the proper aqueous detergent, and the correct hydraulic impact pressure.
Soldiers in field conditions have often used gasoline (a carcinogen) or any other handy petroleum-based solvent (such as kerosene) to clean cosmoline off stored weapons, an effective but dangerous practice.
It is not recommended to use harsh chemical solvents that could strip paint, finishes, or other aesthetic/functional coatings from the gun’s surface. A better solvent is acetone or mineral spirits. Complete instructions can be found on Cosmoline's official site.
All cosmoline cleaning methods create hazardous waste that must be disposed of in the proper manner. Aqueous or solvent cleaning both have accepted methods to dispose of the "sludge" created. It has been reported that talcum powder can be used as an absorbent of Cosmoline by packing the powder around the item to be cleaned and applying sufficient heat to melt the solid film allowing the compound to be wicked from the coated surface into the talcum, which can be scraped off more easily.
- Aqueous Parts Washer Application "Cosmoline Removal" Retrieved on June 2, 2015
- "CDC – NIOSH Pocket Guide to Chemical Hazards – Gasoline". www.cdc.gov. Archived from the original on 16 October 2015. Retrieved 3 November 2015.
- Step by Step Guide to removal of Cosmoline from firearms 
- Surplusrifle Forum "Mauser stock question" Retrieved on 08 March 2015.
- Salecker, Gene Eric (2008). Rolling Thunder Against the Rising Sun: The Combat History of US Army Tank Battalions in the Pacific in World War II. Mechanicsburg, PA: Stackpole Books. pp. 13 and 18(?). ISBN 9780811703147. OCLC 170058124.